1. Field of the Invention
This invention relates to novel functionalized benzocyclobutenones (BCBOs) and to polymers derived therefrom.
A variety of modified polymers or toughened polymer blends can be produced in reactive processing such as molding, casting and melt blending, through the reactions of certain functional groups. For example, maleic anhydride-modified polyolefins or oxidized poly(phenylene oxide)s are reactive targets in these processes for covalent linkage with nylons. Acetylene may be introduced as a reactive end group into high-performance polymers such as NASA's LARC polyimides. It reacts to cause rapid crosslinking of the polymer at elevated temperatures without the evolution of volatiles during molding or melt processing.
2. Description of the Prior Art
In the late 1970s, Kirchhoff et al at the Dow Chemical Company initiated a research program on the use of benzocyclobutenes in polymer synthesis and modification. The first patent describing the use of benzocyclobutenes in the preparation of high molecular weight polymers was issued in 1985.1! Similar work was independently by Tan and Arnold.2! Since these initial discoveries, the field of benzocyclobutene polymers has rapidly expanded to include more than 50 patents and numerous papers.3!
Benzocyclobutene can be viewed as a latent functional group that upon thermal activation can generate the highly reactive diene (o-quinodimethane), which can then enter into a wide variety of dimerization, oligomerization and Diels-Alder cycloaddition reactions. Thus, the basic technology based on benzocyclobutenes involves a family of thermally polymerizable monomers which contain one or more benzocyclobutene groups per molecule. Heating a bisbenzocyclobutene monomer without a dienophile (olefin or acetylene) leads to a highly crosslinked polymer. The AB monomer containing a benzocyclobutene and a vinyl group yields a linear Diels-Alder cycloaddition polymer upon thermolysis. The benzocyclobutene group is mainly used in a small amount as either an end group or a pendant group. Thus, it has been incorporated into high-performance polyimides, aromatic polyamide and poly(arylene ether)s. A variety of AB monomers have been synthesized and thermally cured to make polymers and composites for aerospace and electronic applications.
Although the benzocyclobutene chemistry is fascinating, the area of its application is confined due to its limited types of interpolymer coupling reactions (just dimerization and Diels-Alder cycloaddition). Accordingly, only dienes can be used as comonomers to produce linear thermoplastics. Other commercial materials such as diols and diamines could not be utilized, because of many unpredictable side reactions with the o-quinodimethane intermediate. In addition, the applications of this chemistry to vinyl polymers and polyols are scarce, as a few reports on the modification of polystyrene have appeared.4!
Benzocyclobutenone (BCBO), similar to but different from benzocyclobutene, can be prepared in several ways.5! Some substituted analogues, including 3-methyl-, 3-methoxy-, 4-methyl-, 4-methoxy-, 5-methyl-, 5-methoxy, 6-methyl-, 4,4-dimethyl-, 3,6-dimethyl-, 3,6-dimethoxy, 3-methoxy-6-methyl-, 3-methyl-6-methoxy-, 3,4,5-trimethyl-, 3,4,5,6-tetramethyl-, 3,6-dimethoxy-4, 5-dimethylbenzocyclobutenones are known.6!
Benzocyclobutenone is also known to undergo the reaction with methanol and cycloaddition reactions with aldehyde and dienophiles such as maleic anhydride and dimethyl fumarate upon flash photolysis.6d,7!
An isocoumarin as a dimer of benzocyclobutenone is also isolated from the reaction of o-(trimethylsilylmethyl)benzoyl chloride with cesium fluoride in refluxing acetonitrile.7!